It’s no surprise to hear that a bug or two is hiding in our house—sooner or later we tend to come across that errant spider that seems to be lost, hanging in our perfect home—yet it seems we have even more company than we can readily see.

The research turned up 579 different types of arthropod, with the average domicile containing anywhere from 32 to 211 kinds. Spiders and beetles, we’ve already heard about—but ants, flies, and book lice are also regulars.

Bertone adds, “While we collected a remarkable diversity of these creatures, we don’t want people to get the impression that all of these species are actually living in everyone’s homes…”Many of the arthropods we found had clearly wandered in from outdoors, been brought in on cut flowers or were otherwise accidentally introduced. Because they’re not equipped to live in our homes, they usually die pretty quickly.”

An example of such a bug would be gall midges (Cecidomyiidae), which despite being found in every home studied, really need outdoor plants and are doomed indoors.

Cecidomyiidae (Gall midge)

However, of the 554 rooms investigated, only five didn’t hold any arthropods.

“We think our homes are sterile environments, but they’re not,” says Bertone, “We share our space with many different species, most of which are benign. The fact that you don’t know they’re there only highlights how little we interact with them.”